The present invention relates to the fabrication of integrated circuits. More particularly, the present invention is directed toward a plasma reactor which provides dynamic inductive and capacitive coupling control for improved performance.
Inductively coupled plasma reactors are known for high density plasma (HDP) processing that includes etching, chemical vapor deposition, and so forth. Examples of such reactors are found in commonly assigned U.S. Pat. Nos. 5,919,382, 5,888,414, 5,614,055, and 5,540,800. Inductively coupled reactors often employ a coiled antenna wound around or near a portion of the reactor chamber and connected to an RF (radio frequency) power source to couple RF energy inductively into the reactor. These reactors typically provide independent control of high density ion generation and ion energy. For example, in some HDP reactors, ion density is primarily controlled by adjusting the RF current in the antenna, while ion energy is primarily controlled by a separate RF power, usually called RF bias, connected to the wafer pedestal.
The voltage in the antenna also produces capacitive coupling to the plasma, which can cause plasma potential oscillation, thereby widening the ion energy distribution. The capacitive coupling may further cause excessive ion bombardment on the chamber wall adjacent the antenna, resulting in an increase in chamber wear and the amount of contaminant particles. Faraday shields have been placed between the antenna and the plasma to suppress capacitive coupling of the RF antenna, as disclosed, for example, in U.S. Pat. Nos. 5,888,414, 5,614,055, and 5,540,800.
The removal of the capacitive coupling of the RF antenna in HDP reactors may make it more difficult to ignite a plasma and maintain a stable plasma in some cases. For instance, the bias RF energy applied to the wafer pedestal often does not provide adequate energy to ignite the plasma if the RF antenna""s capacitive coupling is removed by a Faraday shield.
Numerous plasma reactor designs that include both electrodes and coils have been proposed. For example, one system includes an auxiliary electrode for providing capacitive coupling of RF energy to ensure reliable plasma ignition. Another system employs a pair of parallel capacitive electrodes facing each other in the chamber and an inductive coil wound around a portion of the chamber. Another system includes a coil antenna and a generally planar ceiling electrode which is substantially the same in diameter as the wafer held in the wafer pedestal in the chamber.
There is still a need for a method and an apparatus for controlling the inductive coupling and capacitive coupling in a plasma reactor to achieve improved plasma stability and ignition reliability while reducing erosion and contamination.
The present invention provides a system and a method for dynamic control of the capacitive coupling and inductive coupling of energy into a plasma processing chamber to improve plasma substrate processing, as well as for achieving contamination and defect reduction.
The invention provides an inductive coil for electromagnetically coupling RF energy into the process chamber. The capacitive coupling of the inductive coil into the chamber is desirably suppressed using a Faraday shield or by increasing the spacing between the inductive coil and the chamber wall. An electrode is provided to capacitively couple energy into the chamber. By suppressing the capacitive coupling of the inductive coil and controlling the energy supplied to the electrode, the capacitive coupling into the chamber can be precisely controlled. In a specific embodiment, the same power source is used to supply energy to the inductive coil and the electrode. A coupler is used to apportion the energy supplied to the inductive coil and the electrode.
In specific embodiments, the relative amounts of capacitive and inductive energy provided to the plasma can be dynamically adjusted at ignition and/or during processing, desirably in real time using a computer control system. The conditions such as temperature and pressure may be changed or the process gas mixture may be altered during processing, for instance, for etching or depositing a single layer or different layers on a substrate. Similarly, different amounts of capacitive coupling and inductive coupling may be desirable for maintaining a stable plasma. Parameters that would produce a stable plasma may be predetermined for specific processing conditions, and subsequently used as input to a computer program to control the plasma to enhance plasma stability and process optimization.
Sensors may be provided to monitor the power supplied to the electrode and the inductive coil to provide feedback to a controller which is used to control the RF power levels to adjust the inductive coupling and capacitive coupling in real time. Dynamic inductive and capacitive coupling control produces improved process conditions for achieving reliable plasma ignition, maintaining plasma stability, and enhancing other process characteristics.
Furthermore, to minimize erosion and contamination, the chamber wall adjacent the inductive coil is made of a material that is highly erosion-resistant. On the other hand, the chamber wall adjacent the electrode is made of a material that produces essentially no particles and contaminant compounds from erosion.